Altogether it's seen more Hollywood chases than most studio back lots. Like so much on screen, of course, this incredible stretch of concrete canyon is not what it appears to be. In fact, this familiar backdrop is the Los Angeles River.

Once the very lifeblood of the old pueblo of Los Angeles, the river today seems to many Angelenos to have been engineered into marginal inconsequence - simply a giant storm drain or the butt of talk-show jokes.

Yet as the rest of the nation watches Californians struggle to ensure an adequate supply of electricity, how people here choose to manage their river may well determine whether the 10 million residents of Los Angeles County will have enough of a commodity far more basic to sustaining their lives and economy: water.

To understand the struggles it is necessary to understand something of the river's history.

When the first Spanish explorers came upon it in August 1769, the river appeared a pleasant stream meandering through stands of cottonwoods, alders, sycamores, oaks, and walnuts. Steelhead trout could be taken from its waters. Pronghorn antelope, grizzly bears, and cougar were common. Overhead soared scores of different birds, including the giant Condor.

That promise of plentiful water and fertile land was enough to attract a group of 45 settlers from Mexico in 1781. As the new pueblo grew and prospered, however, the settlers discovered their river was more than a placid stream.

Even today, constrained as it is, the Los Angeles can be a dangerous body of water, says Doug Shure of Friends of the L.A. River.

During its 51-mile journey from the San Fernando Valley to the Pacific, the Los Angeles drops about the same amount in altitude as the Mississippi does in more than 2,200 miles.

Flood velocities in the modern channel can approach 30 feet per second and, with less than three feet of water, it packs enough punch to "flush a car" all the way to the ocean.

What the early settlers were to learn was that they had built on a vast sloping flood plain and the river - swollen by seasonal rains and runoff from the mountain ranges to the east - could have a mind of its own.

River's flooding days were numbered

Real trouble came in 1815, when the flooding Los Angeles washed away the town plaza and, more importantly, changed its course. Where it had flowed westward through what is now downtown, eventually emptying into Santa Monica Bay, it suddenly shifted its mouth miles farther south down to San Pedro Bay. Later flooding would change the river's course again and again until it finally settled on its present site at Long Beach.

By 1904, the growing city's need for water had outstripped the supply from both the river and local aquifers, and development had sprouted along both sides of the river.

Moreover, the city was now largely populated by Easterners who expected rivers to behave as predictably as they generally did in New York or Ohio.

The seasonal threats of the Los Angeles were a challenge to a duel; and in the fight to "tame" Mother Nature, America's choice of weapon well into the 20th century was heavy civil engineering.

From the Brooklyn Bridge to the Panama Canal, there was nothing, it seemed, that iron, steel, and concrete couldn't handle. No surprise then that severe flood damage in 1914 brought the first talk of channelizing the river and the establishment of a flood-control district.

Even deadlier flooding in the 1930s which claimed more than 100 lives made channelization a reality. By the 1960s, the natural Los Angeles River had, for all practical purposes, disappeared, replaced by a massive concrete box channel. Flooding was largely controlled.

But it wasn't a perfect solution. Impressive as it was, the channel was just plain ugly and construction had decimated native plant and animal species.

Development and channelization combined to change the nature of pollution and debris flowing into the Pacific. Plastic bags, oils slicks from city streets, and urban detritus replaced more easily digested silt and uprooted vegetation. Beaches were fouled and coastal waters seriously polluted, threatening the lucrative tourist trade.

In recent decades, the Los Angeles has been the subject of legal battles between environmentalists eager to return the river to something approaching its natural state and flood-control officials equally determined to prevent the devastation which, they were certain, would be the consequence of demolishing its concrete liner.

Even though the struggle had begun to resemble an endless Ping-Pong match, pressures were growing for solutions that seemed beyond the range of either side's thinking.

The public wanted more open space for recreation and the river seemed to many like a good candidate. Environmental groups had already been active in establishing bike paths and parks.

On the other hand, in part because of Los Angeles's astounding growth, the area was facing potentially serious long-term supply shortfalls.

Water from the Owens Valley and the Colorado River was being held back or diverted to other users. Some ground water sources had become polluted and unfit for human consumption.

Additional runoffs pushed the river's limit

Yet seasonal flows through the L.A. River had actually increased substantially over the years, in part because the original channel plans had not fully taken into account the massive increase in runoff generated by development of the San Fernando Valley.

This left local flood-control authorities only two choices: build a huge reservoir to contain the added runoff or raise the channel walls. Either way it meant more concrete.

But maybe there was another way of looking at things. To Andy Lipkis, an urban forester and president of the environmental group The Tree People, hope lay in considering the river as the last link in a vast, largely urban watershed.

If more water could be contained on the land and runoff reduced, then the twin goals of conservation and runoff reduction might be met without resort to more construction.

Certainly, there was historical precedent. Wasting water in California is taken so seriously that it is expressly forbidden by the state's Constitution. Even in the heyday of channelization, when the goal was to move water in and out as quickly as possible, conservation had been a consideration.

Proof of the concept came in the form of a house on a quiet, tree-lined street in South Central Los Angeles, specially modified by the TREES (Transagency Resources for Economic and Environmental Stability) project.

Though barely noticeable, the front and back yards were depressed slightly and bermed to contain rain water. Special cisterns stored a sizable portion of runoff from the roof that would later irrigate the lawns and flowers. Dry wells caught water spilling off the driveway.

In one test, the property contained every drop of an artificial flash flood of 4,000 gallons in 10 minutes.

The results impressed Carl Blum, then the deputy director of The Los Angeles County Department of Public Works - and often seen by many in the environmental community as one of their chief adversaries.

Yet Mr. Blum was a former Eagle Scout and loved the environment. Even if all the TREES's house techniques wouldn't be appropriate everywhere in L.A. County, Blum felt, the project showed alternative methods could work.

Both men quickly realized a major shift had begun. And it spread rapidly. Los Angeles County created a new Watershed Management Division and its new deputy director, Rod Kubomoto, has seen how that change has affected operations.

"In the past you'd have severe street flooding and the typical solution was put a pipe in the ground. That was that. Today we look at it differently. Maybe we build a park - multi-use during the good season [and a containment area during the winter rains]. But we take it a step further and look at water quality issues, vegetation, habitat, and wildlife needs.... You base everything on the principal that water is a valuable resource."

A larger-scale project to reduce flooding in an area of Sun Valley using some of the new techniques is under way. The new paradigm also seems to have energized all concerned. Engineers and environmentalists have begun to talk to each other and call upon each other's expertise.

Planning now involves large numbers of "stakeholders" - including individual property owners; the Army Corps of Engineers; recreation departments; police and fire services; economic planners; engineers; and an alphabet soup of coalitions, conservancies, and regulators.

The broader thinking implicit in the watershed management paradigm has forced these groups not only to work together but to consider the long-term consequences.

A new park might seem like a good idea, but what about noise levels for nearby residents? How will it affect local businesses? Will it attract gangs? Who is going to pay for it? Each situation presents its own set of problems.

"All of these issues need to be dealt with," says Blum, now vice president of the Los Angeles and San Gabriel Rivers Watershed Council and still a dedicated engineer. "They are complicated and no one size fits all."